1. Field of the invention
This invention relates to a method for collectively receiving at a high voltage and distributing at a low voltage, and collective housing using the same, which is capable of suitably distributing power by considering power consumption changes in each household.
2. Description of Prior Art
In collective housing such as apartments, generally each household makes a usage based electricity contract with an electric power company and is supplied low voltage electricity (for example 200 V, 100 V). This is referred as a method for individually receiving at a low voltage. On the other hand, there is a method for receiving electricity at a high voltage by an electricity contract for industry (for example 6000 V) and distributing and supplying electricity at a low voltage (for example 200 V, 100 V) to each household. It is referred as a method for collectively receiving at a high voltage and distributing at a low voltage. Following is a difference between the method for individually receiving at a low voltage and the method for collectively receiving at a high voltage and distributing at a low voltage.
FIG. 1 is a schematic view illustrating an example of power supply to a detached house. Power at a low voltage (100 V or 200 V) is distributed from an electric power company through a power system 200 to a household 201 via a current limiter (referred as a breaker hereinafter).
Power is distributed not through a breaker in some contracts. However, it depends on an electric power company whether a breaker is equipped or not. Following explanation is in the case that the breaker is equipped.
A contract for supplying electricity to a detached house at a low voltage is referred as an electricity contract. In this case, a voltage is constantly 100 V, and a contracted power capacity is expressed by a current value, referred as a contracted current. The contracted current is determined on the basis of a maximum demanded current.
The maximum demanded current is a maximum volume of a demanded current consumed in a certain period in a certain area. In the example of FIG. 1, it is determined by a total current necessary for using loads (such as a television, air conditioner, rice cooker, washing machine, and refrigerator) in a household simultaneously. The household makes a contract of a contracted current, which satisfies a maximum demanded electric current, with an electric power company, and a breaker for controlling the contracted current is provided by the electric power company. A maximum current capacity is a maximum value of power enabling the household to use under the contract within a range of the contracted electric current, and is equivalent to a contracted electric current in the above mentioned electricity contract.
FIG. 2 is a schematic view illustrating an example of power distribution by using the method of collectively receiving at a high voltage and distributing at a low voltage in collective housing such as apartments or a group of detached houses. Power at a high voltage for example 6000 V is collectively received by a power distribution device 300 from an electric power company, and is distributed from the power distribution device 300 to each household 13a . . . at a low voltage for example 100 or 200 V. A base rate is determined on the basis of the contracted current in a usage-based electricity contract. On the other hand, a base rate in a power contract for industry is determined on the basis of a contracted power. The contracted power is determined on the basis of a maximum demanded power which a user can consume at one time under a contract (referred as a maximum power capacity hereinafter). In an actual case, the maximum demanded power in the past twelve months is a contracted power.
FIG. 3 is a schematic view illustrating an example of an electrical structure of the method for collectively receiving at a high voltage and distributing at a low voltage. The power distribution device 300 includes a high voltage trance 300a, a high voltage ac load switch 300b and so on. The power distribution device 300 distributes power at a low voltage (100 or 200 V) to each household 13a . . . through a breaker 130. A total contracted capacity of such the collective housing is not always equal to a value obtained by multiplying a maximum capacity per household by the number of households, because it is not likely that all the households use electricity at maximum at the same time. Thus, a concept of a demand factor is employed. A total contracted power of the collective housing using the method for collectively receiving at a high voltage and distributing at a low voltage can be expressed as follow.
Contracted power of all the households in the collective housing (W)=maximum current capacity per household (for example 30A)×100 V×the number of households×demand factor(%)
The demand factor can be obtained from;
Demand factor (%)=maximum demanded power (kW)/rated capacity of equipment Σ(kW)×100
The above demand factor is assumed to be 40% in the collective housing having more than 20 households from an empirical rule.
FIG. 4 is a diagram for comparing an amount of power used in a month and an electricity bill per household in introducing the method for collectively receiving at a high voltage and receiving at a low voltage and the method for individually receiving at a low voltage to the collective housing of 50 households in an area of the electric power company employing an ampere bill system (for example a bill system adopted by Tokyo Electric Power Company and Tohoku Electric Power Company). As shown in FIG. 4, a minimum charge in the method for individually receiving at a low voltage is smaller than the base rate in the method for collectively receiving at a high voltage and receiving at a low voltage. A base rate in the method for collectively receiving at a high voltage and receiving at a low voltage becomes small as a contracted current is small. In the cases 1 and 2 in FIG. 4, the base rates are approximately 2000 yen and 1300 yen respectively.
An electricity bill in total is a sum of a base rate (or a minimum charge) and usage based charge in both cases. It is noted that a unit charge per kWh in the usage based charge is larger in the method for individually receiving at a low voltage. In addition, in the bill system of the method for individually receiving at a low voltage, a unit charge in the usage-based charge system increases when an amount of power consumed exceeds a certain level.
In the method for collectively receiving at a high voltage and distributing at a low voltage, a unit charge per kWh is smaller than that in the method for individually receiving at a low voltage, and even when a consumed power amount increases, a unit charge does not change as not like in the case of the method for individually receiving at a low voltage.
As shown in FIG. 4, electricity bills per household in the method for collectively receiving at a high voltage and distributing at a low voltage (Case 1) and the method for individually receiving at a low voltage are coincident at the A point, which is a breakeven point. A amount of electricity consumed in an average household is on the B point, at which an electricity bill increases in the method for individually receiving at a low voltage, rather than the A point, thus the method for collectively receiving at a high voltage and distributing at a low voltage is more economical. In the case 1, a difference in bills is 1,231 yen.
Then, the contracted current per household in the method for collectively receiving at a high voltage and receiving at a low voltage reduces from 30 A (the Case 1) to 20 A (Case 2). The breakeven point shifts from the A point to the A′ point. Because the B point does not change, a difference in bill between these methods further increases.
As described above, as long as the amount of power consumed in a month is not smaller than an amount at the breakeven point, an electricity bill charged in the method for collectively received at a high voltage and distributing at a low voltage is more economical than the method for individually receiving at a low voltage. Therefore, in the collective housing, the method for collectively received at a high voltage and distributing at a low voltage has an advantage in terms of an electricity bill than the method for individually receiving at a low voltage.
In addition, the electricity bill can be reduced when a contracted electric current is smaller in the method for collectively received at a high voltage and distributing at a low voltage.
In the collective housing, however, a situation in using electricity and an amount of consumed power are different from each household. Thus, if a contracted current is made small for all the households, some of the households may have troubles in using electricity. Accordingly, a power contract with a sufficient contracted current is inevitable in an actual situation.